Radar attenuation demonstrates advective cooling in the Siple Coast ice streams

• Published in: Journal of Glaciology
• Main Authors: Benjamin H. Hills, Knut Christianson, Robert W. Jacobel, Howard Conway, Rickard Pettersson
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press 2023
• Subjects: Ice dynamics; Ice streams; Ice temperature; Radio-echo sounding; Environmental sciences; GE1-350; Meteorology. Climatology; QC851-999; Bindschadler Ice Stream; Kamb Ice Stream; Siple; Siple Coast; Whillans; Whillans Ice Stream; Journal of Glaciology
• Online Access: https://doi.org/10.1017/jog.2022.86; https://doaj.org/article/683b049a77ce49d68e1aeb41d02ba282

Ice streams are warmed by shear strain, both vertical shear near the bed and lateral shear at the margins. Warm ice deforms more easily, establishing a positive feedback loop in an ice stream where fast flow leads to warm ice and then to even faster flow. Here, we use radar attenuation measurements to show that the Siple Coast ice streams are colder than previously thought, which we hypothesize is due to along-flow advection of cold ice from upstream. We interpret the attenuation results within the context of previous ice-temperature measurements from nearby sites where hot-water boreholes were drilled. These in-situ temperatures are notably colder than model predictions, both in the ice streams and in an ice-stream shear margin. We then model ice temperature using a 1.5-dimensional numerical model which includes a parameterization for along-flow advection. Compared to analytical solutions, we find depth-averaged temperatures that are colder by 0.7°C in the Bindschadler Ice Stream, 2.7°C in the Kamb Ice Stream and 6.2–8.2°C in the Dragon Shear Margin of Whillans Ice Stream, closer to the borehole measurements at all locations. Modelled cooling corresponds to shear-margin thermal strengthening by 3–3.5 times compared to the warm-ice case, which must be compensated by some other weakening mechanism such as material damage or ice-crystal fabric anisotropy.